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390 professor of animal morphology at Cambridge. From 1890 to 1907 he held a readership in that subject himself, and in 1907 became professor of zoology in Cambridge University. Two years later he was transferred to the Imperial College of Science and Technology in the same capacity. Details of his work in cytology and embryology are to be found in 7.720, 9.320 and 328. He died in London Feb. 27 1913. SEEBOHM, FREDERIC (1833-1912), English historian, was a native of Bradford and came of a Quaker family. His interest in problems of modern life, social and religious, led him to study the conditions of English rural life in the past and the religious move- ments of the Reformation. In his English Village Community (1853) he dwelt on the survival of Roman influences in agricultural life; and in his Tribal Systems in Wales (1895) he reconstituted a Celtic society from I4th century evidence. He died at Hitchin Feb. 6 1912. SEELY, SIR CHARLES, 1ST BART. (1833-1915), British politician was born at Lincoln Aug. 1 1 1833. He came of a family which held large property, including coal-mines, in the Midlands, and also in the Isle of Wight. In 1869 he entered the House of Com- mons as Liberal member for Nottingham, but lost his seat at the general election of 1874. He was reelected in 1880, but seceded from the Liberal party on Irish Home Rule, and in 1885 lost his seat. He was once more elected in 1892, and held the seat until 1895. In 1896 he was created a baronet. Sir Charles Seely was a warm supporter of the Volunteer movement. He died suddenly at Brooke House, Isle of Wight, April 16 1915.

His youngest son, JOHN EDWARD BERNARD SEELY (1868- ), British politician, was born at Brooke Hill Hall, Derbyshire, May 31 1868. Educated at Harrow and Trinity College, Cambridge, he was called to the bar in 1897, and from 1900 to 1001 served with the yeomanry during the South African War. In 1900 he entered the House of Commons as Liberal member for the Isle of Wight, but was defeated at the 1906 election. He was, however, elected the same year for the Abercromby division of Liverpool. In 1908 he entered the Asquith Government as Under-Secretary for the Colonies, but in 1910 lost his seat, although in the second general election of that year he stood successfully for the Ilkeston division of Derbyshire. In 1911 he was made Under-Secretary for War, and in 1912 became War Minister. Owing, however, to the events attending the Curragh incident of 1914, he resigned in the summer. He served in the army with distinction in the World War, rising to the rank of general in 1918, and on his return to official life be- came parliamentary under-secretary to the Ministry of Munitions and deputy-Minister of Munitions (1918). In Jan. 1919 he became Under-Secretary for Air, and president of the Air Council, but re- signed in Nov. of the same year. SEGUR, PIERRE M. M. H., MARQUIS DE (1853-1916), French author (see 24.584), died at Poissy Aug. 13 1916.

SEISMOLOGY (see 8.817 and 24.589). Strictly speaking, seismology is that department of knowledge which is concerned with the study of earthquakes, and such was its meaning up to the end of the igth century, the older seismology being exclu- sively concerned with the earthquake which could be felt. In the early nineties it was discovered that suitably designed and sufficiently sensitive seismometers recorded disturbances which were evidently connected with great earthquakes, and, as it was known that the intensity of disturbance decreased with an in- crease of distance from the central region of greatest violence, it was natural to conclude that the very small disturbances, registered at great distances, were due to the same cause that gave rise to the destructive earthquake. With the accumulation of observations difficulties began to arise; it was found that neither the magnitude of the disturbance, nor the distance at which record could be obtained, bore any constant relation to the magnitude of the earthquake. Some shocks of great violence gave small records, not very extensively distributed, while others of much less severity at the place of origin gave much larger records and were registered all over the earth. The distant records, however, continued to be regarded as records of the earthquake itself, and are still generally described as such. In 1909 R. D. Oldham, when examining the circumstances

of the Californian earthquake of 1906, arrived at the conclusion that the fractures and dislocations of the surface rocks, which gave rise to the destructive earthquakes, were but a secondary consequence of a deep-seated disturbance, to which he gave the name of bathyseism, and suggested that this, and not the earth- quake, was the origin of the disturbance which, propagated through the interior of the earth, gave rise to the long-distance records, commonly known as seismograms. Subsequent con- sideration of other earthquakes confirmed his belief in the cor- rectness of the conclusion, and from this it results that the word "seismology" is at present being used to cover two distinct and independent departments of study, which may be distinguished as leleseismology (rrjXt, distant) or the study of the long-distance records, and engysseismology (lyyvs, near) or the study of the earthquake proper, each being distinct and independent offshoots of the bathyseism, or deep-seated disturbance. It is the first of these which, at the present day, is more especially meant by seismology, and it is an instance of the way in which words gradually depart from their original meaning, that the term should have come to imply something which has no direct connexion with earthquakes.

Nothing is known at present of the origin of the bathyseism, and very little of the depth at which it originates. The latter probably varies considerably, those disturbances which give rise to well-marked teleseisms and moderate surface earthquakes taking place at greater depths than others which are accompanied by violent and destructive earthquakes. The only suggestion which has yet appeared of the depth of origin is by Dr. G. W. Walker, who has followed up certain investigations, started by Prince Boris Galitzin, of the angle of emergencies of the wave-paths, and finds that in many cases they indicate an origin at a considerable depth (it may be as much as 1,200 km.) below the surface. These investigations require following up before they can be accepted as conclusive, but the suggestion is of interest; there is no inherent impossibility, and it seems to offer a possible explanation of some difficulties which have arisen in the interpretation of the long-distance seismograms.

Since 1910 many improvements in detail have been made in the instruments used for obtaining the long-distance records of the newer, or tele-, seismology, and an entirely new principle was introduced by the late Prince Boris Galitzin for a direct measurement of the acceleration of the true motion of the ground. This instrument is based on the fact that, if a plate of quartz is subjected to pressure between two sheets of metal, a free electric charge appears in those sheets, the amount of which is proportioned to the pressure. An instrument was actually constructed on this principle and subjected to experimental tests, but has not been applied to the recording of natural disturbances, owing to the death of the inventor and the effects of the political revolution in Russia.

The rate of propagation of wave-motion through the earth, as registered by long-distance seismographs, has been investigated by Dr. C. G. Knott, who has succeeded in solving the mathematical difficulties of the problem. He finds that the rate of transmission of both the first phase, condensational, and of the second phase, distortional, waves increases continuously till the wave-path attains a depth of about three-tenths of the earth's radius, the wave-paths reaching lesser depths than this having a continuously curved form, convex towards the centre of the earth. Beyond this the rate of propagation is nearly constant, even decreasing at certain depths so that some of the wave paths are concave towards the centre in part of their course. Below sixtenths of the radius the distortional wave is killed out, and is not registered at distances greater than 1 20 from the epicentre. The rate of propagation of the two forms of wave-motion is about 7-2 and 4-0 km. per second respectively, near the surface of the earth, and about 12-8 and 6-8 at depths of over 1,500 kilometres.

For the older seismology or study of earthquakes proper,, see GEOLOGY (section Dynamical Geology).

AUTHORITIES. The best general introduction to the newer seismology is Dr. G. W. Walker, Modern Seismology (1913). The most complete is by Prince B. Galitzin, original in Russian; a German translation, Vorlesungen in Seismometrie, appeared in 1912. G. W.